Lancet

ABSTRACT

A skin pricker has a barrel ( 1,11 ) in which a hammer ( 2,29 ) released by a trigger mechanism ( 32,34 ) can be shot forwards by a compressed spring ( 3,38 ) to impact on a lancet ( 24 ) and momentarily project its tip. The rear end of the spring acts against a barrier ( 4,39 ) adjustable axially of the barrel, so that the spring can be more or less compressed before release, causing the hammer to act with greater or lesser force on the lancet. The barrier ( 4,39 ) may have projections ( 6,8,42 ) that engage in skew slots ( 7,9,43 ) in the barrel, so that rotation of the barrier axially adjusts it. A sleeve ( 44 ) over the rear part of the barrel instrumental in priming the device may co-operate with the projections and be rotatable to set the desired spring force.

BACKGROUND OF THE INVENTION

This invention relates to medical skin piercing devices.

DESCRIPTION OF THE RELATED ART

Many skin prickers have a spring-operated mechanism that projects thetip of a lancet from a leading end of a barrel. The device is heldagainst the user's skin and “fired”.

Usually the springs have a set rate and the force with which the lancetis urged forwards is always the same for the particular device inquestion. But that is not ideal. For example some skins can be verytough, while others, particularly of infants, can be very soft andeasily pierced. Therefore it is desirable to have available deviceswhich can cope with such variations.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a medical skinpiercing device comprising a barrel, means for carrying a lancet in theforward part of the barrel to allow the tip of the lancet to advancefrom a retracted to a projection position, a hammer arranged whenreleased from a rearward position to act on the rear of the lancet tocause such advance, a barrier to the rear of the hammer and adjustableaxially within the barrel by cam action as a result of rotation, aspring acting between the barrier and the hammer, and a triggermechanism for holding the hammer in, and releasing it from, saidrearward position with the spring compressed to a degree determined bythe axial adjustment of the barrier.

Conveniently, the barrel has slots skew to the axis of the barrel inwhich projections on the barrier engage. The slots may have shortportions non-skew to said axis to locate the projections in setpositions. These projections may be on resilient formations integralwith the barrier, allowing the projections to be moved radially inwardsfor insertion of the barrier into the barrel, the projections springingoutwardly when they register with the slots.

Preferably, the rear portion of the barrel is encased by a captivesleeve spring urged forwardly, the sleeve having a lost motionconnection through the rear end of the barrel and through the barrier tothe hammer, whereby pulling back the sleeve retracts the hammer to saidrearward position, and release of the sleeve allows the sleeve to revertto its forward position disconnected from the hammer. The sleeve whenpulled back may reveal the slots for adjustment of the projections inthe slots, but preferably it will co-operate with at least one saidprojection and be rotatable to adjust the barrier.

A nose section of the barrel will conveniently be removable to exposethe lancet carrying means and allow lancets to be removed and replaced.These lancet carrying means may be a generally tubular member withlimited axial movement, into which a lancet fits from the forward endand spring urged rearwardly normally to maintain a lancet tip retracted.

To avoid handling a lancet after use, an ejector rod can extendlengthwise of the barrel through the barrier and the hammer and bemovable forwards to eject a lancet from the carrying means when the nosesection is removed.

For a better understanding of the invention some embodiments will now bedescribed, by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic side view, partly in section and partly inghost, of a device for adjusting the penetration force of a medicalneedle or lancet, set to a maximum,

FIG. 2 is a cross-section on the line II—II of FIG. 1,

FIG. 3 is a side view similar to FIG. 1 but with the device set to aminimum,

FIG. 4 is a cross-section on the line IV—IV of FIG. 3,

FIG. 5 is a development of a curved slot in the barrel of the device.

FIG. 6 is a side view of a skin pricker,

FIG. 7 is a longitudinal section of the skin pricker, on the lineVII—VII of FIG. 6,

FIG. 8 is a perspective view of a spring force adjuster forming part ofthe pricker of FIG. 6, and

FIG. 9 is a longitudinal section of the rear portion of the pricker ofFIG. 6, the sectional plane being at right angles to that of FIG. 7.

The device of FIG. 1 has a barrel 1 with a hammer 2 loosely plugging itsforward end and urged forwards by a spring 3. There is a triggermechanism (not shown) which holds the hammer 2 in the cocked positionshown. The spring 3 reacts against an axially adjustable barrier 4towards the rear end and when the trigger is operated it shoots thereleased hammer 2 forwards.

The barrier 4 is of thick, disc-like form with a protuberance 5 on itsforward side around which the spring locates. The cylindrical surface ofthe disc, of a radius slightly less than the inner radius of the barrel,has two diametrically opposed projections, one being a cam 6 whichprojects into a part-helical slot 7 in the barrel and the other being asmall stud 8 which co-operates with a part-helical slot 9 complementaryto the slot 7.

The slots 7 and 9 are not smooth sided over their whole lengths. Attheir ends and at their mid-points they divert into flats 10 normalrather than skew to the axis of the barrel. This enables the cam 6 andstud 8 to locate stably at three set positions, the extreme ones beingshown in FIGS. 1 to 4 and the intermediate one in FIG. 5. It would bepossible to have more than one intermediate position.

The barrel 1 is of moulded plastics, giving some elasticity andresilience. This enables the barrier 4 to be pressed into place throughthe rear end of the barrel. It may be convenient to push it in aslant,with the cam 6 leading, and skew to correspond to the angle of the slot7. Then the cam 6 can be worked up, with the adjacent portion of thebarrier 4, into the slot 7, followed by the portion adjacent the stud 8being pushed until the stud registers with the slot 9. The barrier isthen manipulated until it is co-axial with the barrel 1. It will be keptsubstantially square on to the axis by the spring 1, by the cam 6 in theslot 7 and the stud 8 in the slot 9, and by the co-operation of itscylindrical end surface with the inner surface of the barrel (which willhave reverted to its proper shape following any distortion suffered as aresult of inserting the barrier).

The cam 6 is accessible, and the user can shift it along the slot 7 tocause the barrier 4 to increase or decrease the compression of thespring 3. When the barrier is forwards, as in FIG. 1, there is maximuminitial compression, and the hammer 2 is propelled forwards with maximumforce. Correspondingly, when the barrier is rearwards, as in FIG. 3, thehammer is propelled forwards with lesser force.

A practical example is shown in FIGS. 6 to 9 in which a skin pricker hasa cylindrical barrel 11 with a reduced forward end portion 12 over whichfits a connecting collar 13, screwing to the barrel at shoulder 14. Anose piece 15 attaches to the collar 13, being fitted over a reducedforward end portion 16 before being trapped by a non-return formation.But although captive, it can still be rotated, using grip 17, to adjustits axial position within limits. An internal ring 18 determines this,and thereby controls the amount by which a lancet tip will projectthrough aperture 19.

The barrel portion 12 receives and guides a tubular lancet holder 20whose rear out-turned rim 21 is initially held back from the shoulder 14by a light spring 22. At about its mid-length the holder has shallowinternal projections 23 which retain a lancet 24 snapped in from thefront end, and more pronounced external barbs 25 which snap into slots26 in the portion 12 from the rear, allowing limited axial travel of theholder 20. Initially, the tip of the lancet 23 is retracted within thenose piece 15.

An ejector rod 27 extends co-axially through the barrel and beyond tothe rear, and when the collar 13, with the nose piece 15, is removed itcan be pressed by rear end knob 28 to snap the lancet forwardly out ofthe holder 20.

A hammer 29 has a generally cylindrical hollow body through which therod 27 freely passes, and with a cylindrical spigot at its forward endaround which snaps a rubber ring 30. When released, this will hit therim 21 to drive the holder 20 and thus the lancet forwards. This ringdevice serves as a damper and the rubber ensures virtually silentoperation. A narrow U-shaped slot in the cylindrical wall of the hammerforms a flexible finger 31 which, at its free forward end, has anoutwardly projecting stud 32 engaged in a slot 33 in the barrel. This ispart of a trigger mechanism, whose other part is an oval button 34mounted over this region of the barrel and with an inner projection 35that co-operates with the stud 32. Pressure on the button flexes thefinger 31 in to release the stud 32 from the slot 33 and allows thehammer to shoot forwards. The finger 31 can almost immediately recoverits original attitude with the stud 32 entering another slot 36.

At its rear end, the hammer 29 has a short cylindrical extension 37which locates the forward end of a helical drive spring 38, whose rearend reacts against a force adjuster 39.

The force adjuster is best seen in FIG. 8. It has a cylindrical plasticsbody 40, through which the rod 27 will freely pass, and on the outsideof that two diametrically opposed integral loops 41 of arcuate form,each subtending an angle of about 90°. The outer surfaces of the loopsare of a radius corresponding to the interior of the barrel 11 but theloops are thin enough to be deformed radially inwards, to allowoutwardly projecting studs 42 at the centres of those outer surfaces tobe depressed sufficiently to enable the adjuster to be entered into therear of the barrel. When the studs reach opposed inclined slots 43 inthe barrel the loops 41 spring outwards, and the studs are captive.

A sleeve 44 sheaths the rear end of the barrel 11 and provides at itsrear end a guide slot 45 for the knob 28 of the rod 27.

The sleeve 44 is made from two substantially semi-cylindrical halves,one half 46 having at its leading end a recess 47 matching in shape therear part of a low wall 48 proud of the barrel 11 and closelysurrounding the trigger button 34. The sleeve 44 is urged forwardly by ahelical spring 49 around the barrel, acting between a rear end flange 50on the barrel and an annular rib 51 internal of the sleeve. Normally,the spring 49 causes the sleeve 44 to be located with the wall 48nesting in the recess 47.

The ejector rod 27 is reduced to semi-circular cross-section over muchof its length and along this portion lies a complementarily shaped,shorter, loading rod 52 with a certain freedom of axial movementrelative to the rod 27. This has a rear end head 53 which is trapped byinternal webs 54 of the sleeve 44 and it passes through the forceadjuster 39 into the hammer 29, where barbs or spring fingers engage therear wall of the hammer. Initially, both the hammer 29 and the sleeve 44are in their forward positions. But once the lancet has been loaded, thesleeve 44 is pulled back, and the loading rod 52, drawn by its head 53,pulls back the hammer 29, the stud 32 being temporarily pressed inwardsby the bridge between the slots 33 and 36. Then the hammer is trapped inits rearward ready-to-fire position and the sleeve 44 can be allowed tospring forwards, taking the rod 52 with it and freeing the hammer 29 forforward movement.

When the sleeve 44 is in its rearward position, it can be rotated tooperate the force adjuster 39, being turned one way to move the adjusterforwards and increase the initial spring force, and the other way tomove the adjuster rearwardly and reduce that initial force. At least oneof the studs 42 will be proud of the barrel 11 and can be positivelyengaged by a formation within the forward end of the sleeve, behindinturned rib 55. The amount of force adjustment can be gauged by theamount of rotation. Once the sleeve is released to spring forwards, itis guided into its original alignment by the recess 47 meeting the wall48.

The sleeve 44 could be arranged to expose at least one of the studs 42,so that the user could directly manipulate the force adjuster. But thatmight prove awkward in practice.

In these figures the slots in the barrel are shown without flats, buttheir angle is such that the studs will remain where positioned byfriction. But flats could be provided if desired.

1. A medical skin piercing device comprising a barrel, means forcarrying a lancet in the forward part of the barrel to allow the tip ofthe lancet to advance from a retracted to a projecting position, ahammer arranged when released from a rearward position to impact on therear of the lancet to cause such advance, a barrier to the rear of thehammer and user-adjustable axially within the barrel by cam action as aresult of rotation of the barrier, a spring acting between the barrierand the hammer, and a trigger mechanism for holding the hammer in andreleasing the hammer from said rearward position with the springcompressed to a degree determined by the axial adjustment of thebarrier, wherein the user-set degree of compression of the springdetermines the force propelling the hammer after release of the hammer,wherein the barrel has slots skew to the axis of the barrel in whichprojections on the barrier engage, wherein the rear portion of thebarrel is encased by a captive sleeve spring-urged forwardly, the sleevehaving a lost motion connection through the rear end of the barrel andthrough the barrier to the hammer, whereby pulling back the sleeveretracts the hammer to said rearward position, and release of the sleeveallows the sleeve to revert to its forward position disconnected fromthe hammer, and wherein the sleeve when pulled back reveals the slotsfor adjustment of the projections in the slots.
 2. A device as claimedin claim 1, wherein the slots have short portions non-skew to said axisto locate the projections in set positions.
 3. A device as claimed inclaim 1, wherein the projections are on resilient formations integralwith the barrier, allowing the projections to be moved radially inwardsfor insertion of the barrier into the barrel, the projections springingoutwardly when they register with the slots.
 4. A device as claimed inclaim 1, wherein a nose section of the barrel is removable to expose thelancet carrying means and allow lancets to be removed and replaced.
 5. Amedical skin piercing device, comprising a barrel, means for carrying alancet in the forward part of the barrel to allow the tip of the lancetto advance from a retracted to a projecting position, a hammer arrangedwhen released from a rearward position to impact on the rear of thelancet to cause such advance, a barrier to the rear of the hammer anduser-adjustable axially within the barrel by cam action as a result ofrotation of the barrier, a spring acting between the barrier and thehammer, and a trigger mechanism for holding the hammer in and releasingthe hammer from said rearward position with the spring compressed to adegree determined by the axial adjustment of the barrier, wherein theuser-set degree of compression of the spring determines the forcepropelling the hammer after release of the hammer, wherein the barrelhas slots skew to the axis of the barrel in which projections on thebarrier engage, wherein the rear portion of the barrel is encased by acaptive sleeve spring-urged forwardly, the sleeve having a lost motionconnection through the rear end of the barrel and through the barrier tothe hammer, whereby pulling back the sleeve retracts the hammer to saidrearward position, and release of the sleeve allows the sleeve to revertto its forward position disconnected from the hammer, and wherein thesleeve when pulled back co-operates with at least one said projectionand is rotatable to adjust the barrier.
 6. A device as claimed in claim5, wherein the slots have short portions non-skew to said axis to locatethe projections in set positions.
 7. A device as claimed in claim 5,wherein the projections are on resilient formations integral with thebarrier, allowing the projections to be moved radially inwards forinsertion of the barrier into the barrel, the projections springingoutwardly when they register with the slots.
 8. A medical skin piercingdevice comprising a barrel, means for carrying a lancet in the forwardpart of the barrel to allow the tip of the lancet to advance from aretracted to a projecting position, a hammer arranged when released froma rearward position to impact on the rear of the lancet to cause suchadvance, a barrier to the rear of the hammer and user-adjustable axiallywithin the barrel by cam action as a result of rotation of the barrier,a spring acting between the barrier and the hammer, and a triggermechanism for holding the hammer in and releasing the hammer from saidrearward position with the spring compressed to a degree determined bythe axial adjustment of the barrier, wherein the user-set degree ofcompression of the spring determines the force propelling the hammerafter release of the hammer, wherein a nose section of the barrel isremovable to expose the lancet carrying means and allow lancets to beremoved and replaced, wherein the lancet carrying means is a generallytubular member with limited axial movement, into which a lancet fitsfrom the forward end and spring-urged rearwardly normally to maintain alancet tip retracted, and wherein an ejector rod extends lengthwise ofthe barrel through the barrier and the hammer and is movable forwards toeject a lancet from the carrying means when the nose section is removed.